This invention relates to pressure exchangers for transfer of energy from one liquid flow to another. More specifically, this invention relates to pressure exchangers for the transfer of energy from one liquid stream to another using a rotating split rotor exhibiting enhanced/proportional sealing and wear adjustment characteristics.
The present invention provides a device which can be appropriately described as an engine for exchanging pressure energy between relatively high and relatively low pressure fluid systems, which the term fluid being defined here as including gases, liquids and pumpable mixtures of liquids and solids. The engine for pressure energy exchange of the present invention is a highly efficient device with well over 90% of the energy of pressurization in a pressurized fluid system being transferred to a fluid system at a lower pressure. The device employed for achieving this highly efficient transfer has a long and trouble free operating life which is not interrupted by the plugging and fouling of valves, or the binding or freezing of sliding pistons or the like.
In processes where a liquid is made to flow under pressure, only a relatively small amount (about 20%) of the total energy input is consumed in pressurizing the liquid, the bulk of the energy being used instead to maintain the fluid in flow under pressure. For this reason, continuous flow operation requires much greater energy consumption than non-flow pressurization.
In some industrial processes, elevated pressures are required only in certain parts of the operation to achieve the desired results, following which the pressurized fluid is depressurized. In other processes, some fluids used in the process are available at high pressures and others at low pressures, and it is desirable to exchange pressure energy between these two fluids. As a result, in some applications, great improvement in economy can be realized if pressure exchange can be efficiently transferred between two.
By way of illustration, a specific process of this type is the exchange crystallization process for effecting desalination of sea water, or other saline aqueous solutions. In this process, a slurry of ice and an exchange liquid, such as a hydrocarbon, is placed under extreme pressure in order to reverse the order of freezing so that the ice crystals melt, and the exchange liquid is partially frozen. Following this step of the desalination process, the water from the melting of the ice is separated from the hydrocarbon, which is in the form of a slurry of solid hydrocarbon particles with the liquid hydrocarbon, and the separated phases are then depressurized to near atmospheric pressure. The economy with which the exchange crystallization desalination process can be practiced is directly dependent upon the efficiency with which the energy input to the process upon pressurization of the ice-exchange liquid system can be recovered after separation of the water-exchange liquid phases.
Another example where a pressure exchange engine finds application is in the production of potable water using the reverse osmosis membrane process. In this process, a feed saline solution is pumped into a membrane array at high pressure. The input saline solution is then divided by the membrane array into super saline solution (brine) at high pressure and potable water at low pressure. While the high pressure brine is no longer useful in this process as a fluid, the pressure energy that it contains has high value. A pressure exchange engine is employed to recover the pressure energy in the brine and transfer it to feed saline solution. After transfer of the pressure energy in the brine flow, the brine is expelled at low pressure to drain.
Accordingly, pressure exchangers of varying design are well known in the art. U.S. Pat. No. 3,431,747 to Hashemi et al. teaches a pressure exchanger for transfer of pressure energy from a liquid flow of one liquid system to a liquid flow of another liquid system. This pressure exchanger comprises a housing with an inlet and outlet duct for each liquid flow, and a cylindrical rotor arranged in the housing and adapted to rotate about its longitudinal axis. The cylindrical rotor is provided with a number of passages or bores extending parallel to the longitudinal axis and having an opening at each end.
A separation device may be inserted into each bore for separation of the liquid systems. The movement of the separation device is limited due to the use of a seat at each end of the passages. The seats cause a reduction in cross-area of the bores and are susceptible to wear and eventual failure.
Referring to FIG. 3 which shows a cross-section of the prior art exchanger, a major drawback of the prior art is the reduction in sealing surface-area between the inlet and outlet ports. The two ducts are separated by a very thin wall, thereby requiring extremely tight fitting components to ensure an acceptable level of sealing and the prevention of pressure loss between the high and low pressure ports. Leakage between these two ports results in reduced efficiency of the pressure exchanger, and as the tight tolerances of the mechanical components begin to wear, leakage between the ports will only increase and require costly maintenance as shown in FIG. 3. Attempts have been made to incorporate springs and seals at the ends of the passageways to reduce leakage. Due however to the obvious drawbacks of this approach, the seals eventually wear out and or the springs degrade overtime, both of which require expensive downtime and repair. In addition, seals of this nature function properly only when they are aligned with the housing bores. During a single rotation, alignment of the rotor bore and the housing bore occurs only for a brief moment during the cycle. A seal with intermittent sealing capability is undesirable since leakage of high pressure fluid to the low pressure conduit represents a reduction in efficiency of the device.
There therefore is a need for a pressure exchanger which provides both smooth and uninterrupted fluid exchange as well as enhanced sealing capability thereby reducing the amount of leakage that occurs between the high and low pressure ports.